Cost-effective recycling of materials, such as glass, has become an increasingly important issue because of stresses on the environment and scarcity of resources. Concern about these issues has prompted governmental involvement, including the establishment of governmental guidelines, e.g., “bottle bills.” Because of governmental requirements and environmental awareness, American consumers are now recycling at a greater rate than ever before.
Increased recycling of materials reduces the amount of materials, such as glass, plastics, paper, etc., that enters landfills or other waste disposal points. Additionally, recycling significantly reduces the need for manufacturers to use “virgin” materials, and thus preserves environmental resources. Further, the use of recyclables in place of virgin raw materials often reduces energy requirements, eliminates process steps, and reduces waste streams, including air emissions during product manufacturing. For example, recycled glass requires less energy and emits fewer contaminants during the glass manufacturing process than virgin raw materials do. Many states have placed demands on glass manufacturers that require that new glass bottles to contain a minimum percentage of recycled glass. For example, in Oregon, glass container manufacturers are required to use at least 35% post-consumer cullet, which is broken pieces of glass. California has even more aggressive laws, which require glass manufacturers to increase use of recycled content to 65% by 2005.
However, there are associated issues of complying with these governmental mandates. Prohibitive sorting costs have made it difficult for suppliers to process an adequate quantity of single-colored recycled glass. Often, the glass coming into a material recovery facility (MRF) and/or a glass processing facility, e.g., a site where cullet is cleaned and prepared for shipment to glass manufacturers, is broken, contaminated with other materials, and of mixed color. Such material was previously unusable for glass manufacturing and was used in low value applications or simply placed in a landfill. Currently, however, regulatory requirements and other issues are forcing glass manufacturers to increase the amount of mixed-color cullet used in their furnaces.
Generally, fewer problems exist when recycling clean sources of glass cullet which are of the same composition as products being manufactured. However, since most cullet is derived from consumer waste, the main issue is how well-segregated the different glass waste streams are, and the consequent level of contamination. Foreign material such as ceramics (such as pottery and china, from restaurants and/or bars); stones, gravel and/or dirt (from poor storage of cullet); ferrous metals (from bottle tops and other scrap); non-ferrous metals (lead foils from wine bottles or aluminum bottle caps); and organics (labels and excessive food residue) can all render a batch of cullet unusable. Glass manufacturers face several significant issues, a primary one concerns utilizing mixed-color cullet in glass production in order to comply with the new environmental laws.
Glass manufacturers are especially concerned about the quality of glass supplied from post-consumer streams. With glass batch formulations now able to contain mixed cullet (i.e., glass of mixed colors, typically green, amber, and flint), mixed cullet or single-colored glass received by glass manufacturers should consistently meet the specifications given by the suppliers. Glass manufacturers rely upon these specifications, which specify glass compositions and levels of impurities, to develop a glass batch recipe or formulation for manufacturing bottles.
Generally, the glass making operation is a continuous batch process where the cullet is melted and subsequently dissolved with other raw materials necessary to achieve the required final glass composition. The addition of colored cullet affects, amongst other processing variables, the rate of heat transfer and hence the rate at which the glass melts. Thus, each batch may require a different formulation of raw materials to achieve the desired final glass composition and consistent end product quality. Unfortunately, the supplied specifications may not be accurate, and glass manufacturers often have to “guesstimate” batch formulations. For example, “pure” amber cullet from a processor may contain five or ten percent of other colors and impurity specifications for ceramic and organic contamination may be vague approximations. Any discrepancy between the specifications listed and the actual composition of the supplied glass results in glass that is not uniform in color compared to other glasses manufactured from different batches. This practice has been tolerated by the glass industry as long as cullet use levels were low. As cullet usage increases, what is needed is a way to analyze and characterize mixed cullet to ensure that specifications required for glass manufacture are met.
Mixed-color cullet has often been processed and cleaned by entities, such as MRFs and/or processors, before it is shipped to a glass manufacturer. However, the supply of mixed-color cullet still often contains residual contaminants, such as ceramics and other impurities, which have escaped the sorting and cleaning devices. Such impurities within the mixed-color cullet are a serious concern to glass manufacturers and contribute to the inconsistent color and quantity of manufactured glass, if adjustments to the batch formulation are not made. What is needed is a way to determine the component constitution of mixed cullet utilized in glass manufacture, thereby allowing the glass batch formulation to be adjusted accordingly.
One method of using waste glass for glass manufacturing is described in U.S. Pat. No. 4,252,551, entitled, “Method of continuously preparing molten glass utilizing waste glass as part of ingredients.” The '551 patent describes a method of preparing molten glass in a melting tank of the continuous type by utilizing, as part of the ingredients, waste glass, which may be either pulverized cullet of chopped glass fiber, and which may include an organic substance detrimental to the color, or other properties of the molten glass. The waste glass and other raw materials are fed to molten glass in the tank continuously but separately, such that the waste glass is remelted without contacting the unmelted raw materials and that remelting of the waste glass is preceded by burning any organic substance possibly adhered to the waste glass fed to the tank, and the resultant combustion gas is dissipated.
While the '551 patent provides a suitable method of using waste glass that has impurities for glass manufacturing, it does not provide a way to analyze and characterize mixed-color cullet to ensure that specifications required for glass manufacture are met. Nor does the '551 patent provide a way to determine the component constitution of the waste glass prior to its being utilized in the glass manufacturing process.
One method of using mixed colored cullet for glass manufacturing is described in U.S. Pat. No. 5,718,737, entitled, “Method of recycling mixed colored cullet into amber, green, or flint glass.” The '737 patent, herein incorporated by reference, describes how mixed colored cullet glass is recycled into amber colored glass by regulating the additive amounts of amounts of iron, carbon, sulfur, and sulfur compounds in the mixture to impart the desired reddish-brown hue. While the '737 patent provides a suitable method of using mixed colored cullet for glass manufacturing, it does not provide a way to eliminate variability within the batch formulations. One automated real-time method of determining cullet composition is described in U.S. patent application Ser. No. 10/988,019 , entitled “System For And Method of Batch Analysis And Optimization For Glass Manufacturing.”
U.S. Pat. No. 6,230,521, entitled, “Method of recycling batches of mixed color cullet into amber, green, or flint glass with selected properties,” herein incorporated by reference, describes an automated method for recycling mixed colored cullet glass into new glass products. A computer-controlled process identifies the virgin glass raw materials, the desired target glass properties, the composition of a batch of mixed colored cullet, and the quantity of cullet to be used in the glass melt. The computer controlled process automatically determines the proper amounts of raw materials to add to the batch of mixed colored cullet so that recycled glass is produced that has the desired coloring oxides, redox agents, and glass structural oxides in the proper proportion. However, neither the '737 nor '521 patent provide analysis of the composition of mixed-color cullet as it is introduced into the glass manufacturing process in order to ensure end-product uniformity.
Therefore, there exists a need in the art for a method for analyzing and characterizing mixed-color cullet to ensure that specifications required for glass manufacture are met. Further, there exists a need to determine the component constitution of mixed-color cullet utilized in glass manufacture, thereby allowing the glass batch formulation to be adjusted accordingly.